Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$152.40	12.309%	$171.1589	$171.16	$171.15	$171.20
Purchase #2	$222.74	6.642%	$237.5344	$237.53	$237.55	$237.50
Purchase #3	$49.26	3.212%	$50.8422	$50.84	$50.85	$50.80
Purchase #4	$132.69	4.824%	$139.091	$139.09	$139.10	$139.10
Purchase #5	$230.41	12.783%	$259.8633	$259.86	$259.85	$259.90
Purchase #6	$86.83	12.373%	$97.5735	$97.57	$97.55	$97.60
Purchase #7	$35.45	5.740%	$37.4848	$37.48	$37.50	$37.50
7 purchase totals =	$909.78		$993.5481	$993.53	$993.55	$993.60